It is desirable to reversibly wet or de-wet a surface, because this would allow one to reversibly control the mobility of a fluid on a surface. Controlling the mobility of a fluid on a surface is advantageous in analytical applications where it is desirable to repeatedly move a fluid to a designated location, immobilize the fluid and remobilize it again. Unfortunately existing surfaces do not provide adequate reversible control of wetting.
For instance, certain surfaces with raised features, such as posts or pins, may provide a superhydrophobic surface. That is, a droplet of liquid on a superhydrophobic surface will appear as a suspended drop having a contact angle of at least about 140 degrees. Applying a voltage between the surface and the droplet can cause the surface to become wetted, as indicated by the suspended drop having a contact angle of less than 90 degrees. Unfortunately, the droplet may not return to its position on top of the structure and with a high contact angle when the voltage is then turned off.
Embodiments of the present invention overcome these deficiencies by providing an apparatus having a surface that can be reversibly wetted and de-wetted, as well as methods of using and manufacturing such an apparatus.